This invention relates to an apparatus and method for converting an analog input voltage signal into a digital signal.
Generally, an analog-digital converter (hereinafter referred to as "an A-D converter") is not used alone, but as an attachment to a data-processing unit of a computer. The reason is that the data-processing unit carries out arithmetic operation, using signals digitalized by an A-D converter. The A-D converter acting as an attachment to the data-processing unit performs A-D conversion upon receipt of an instruction for said conversion from the data-processing unit. Hitherto, all hardware for A-D conversion has been included in the A-D converter itself, tending to increase its cost. In recent years, it is demanded to reduce the cost of all types of machinery. Thus it has become necessary for the A-D converter, too, to meet such request.
In view of the above-mentioned circumstances, this invention is intended to provide an A-D converter including a method for A-D conversion which comprises a voltage-time period converter (hereinafter referred to as "a V-T converter") in which the voltage level of an analog input voltage signal and the time period of an oscillated output signal have a linear relationship, and wherein an interruption request is made in proper timing to a data-processing unit of a computer system, causing said unit to take over part of the function of A-D conversion hardware in order to decrease the cost of the A-D converter.